This invention relates to magnetic recording apparatus for cameras and more particularly, to magnetic recording apparatus for photographic still cameras.
In commonly assigned copending application Ser. No. 255,693, entitled FILM INFORMATION EXCHANGE SYSTEM USING DEDICATED MAGNETIC TRACKS ON FILM, and filed Oct. 7, 1988 in the name of Robert P. Cloutier et al. there is disclosed a photographic film having a virtually transparent magnetic coating covering the non-emulsion side of the film and dedicated recording areas on the coating for recording information such as film type, film speed, film exposure information and information relevant to the processing and subsequent use (e.g. printing) of the film. The system thus provides for recording of information during film manufacture, reading and/or recording of information during camera use, and reading and/or recording of print related information during photofinishing. In the aforementioned copending application it is specifically proposed that camera information be recorded in spaced tracks preferably outside the image area along the edge of the film.
Reading and writing information on a magnetic coating or stripe on photographic film in a still camera requires solutions to problems different than those encountered in other apparatus. Perhaps the most significant problem is the space limitations in a portable hand held still camera which necessarily must be as compact and light as possible to appeal to the average consumer. Perhaps equally significant, however, is the characteristics of photographic film relative to more common recording mediums such as magnetic tape. Because photographic films are stiffer then magnetic tape and have varying degrees of curl both in the longitudinal and transverse directions depending upon the base materials and number and nature of sensitizing layers and environmental conditions, they present unusual problems in reading and writing information on a magnetic coating or stripe. To provide a reliable read or write signal the magnetic head must remain in close proximity to the magnetic coating. Any distrubances such as variations in film curl can vary the relationship of the head to the coating and decrease the reliability of the signal.
Another problem unique to compact photographic still cameras is that film advance occurs in a short period of time with a limited amount of motion and does not allow the steady state conditions normally associated with magnetic recording. Recording and playback must take place during transient conditions which tend to separate the film from the recording head. For optimum magnetic recording during these conditions, the magnetic head must maintain contact (i.e. within 10 micro-inches) with the magnetic coating.
Techniques for maintaining the desired relationship of the head to a magnetic coating in other apparatus, are not practical for use in a photographic still camera particularly a compact 35 mm camera. For example, in a sound movie camera, a film having a magnetic stripe along one edge is typically moved over a drum and information is recorded by a magnetic head positioned in close proximity to the drum. The drum provides a rigid support for the film, removes film curl and assures a uniform head to film relationship. While such a fixed support such as a sound drum produces satisfactory results, the space limitations in a photographic still camera render it impractical. Also, it is not suitable for the transient conditions described above.
Also, in a still camera system, it is desirable to record information pertinent to and coincident with images because negatives are cut up in photofinishing. In sound movie cameras, recorded information is displaced from the image to achieve continuous motion of the film during recording as compared with intermittent motion during exposure.
Another problem associated with magnetic recording in a compact photographic still camera is lateral displacement of the film during transport and recording caused by tolerance variations in the transport system and/or film edge non-uniformity. To compensate for these conditions which vary in severity from camera to camera, the width of the magnetic coating area dedicated to recording certain information in a track must be wider than would be the case without such lateral displacement. Similarly, equipment which reads the recorded information such as during photofinishing must be capable of reading information from a relatively wide dedicated track.